The present invention is related to semiconductor devices and, more particularly, to highly compact antifuses in integrated circuits.
An antifuse is a device which operates, as the name implies, in the opposite manner of a fuse. The antifuse lies between two conducting lines. If it is unprogrammed, or open, the antifuse forms a high-resistance electrical path. If the antifuse is programmed, or closed, it forms a low resistance electrical path between the conducting lines.
In integrated circuits, multiple layers of interconnecting conducting lines are stacked over each other. With insulating layers between the conducting lines, multilayer interconnect structures are formed. To make the interconnection between the two lowest conducting layers, the first conducting layer, which is typically a doped region in the integrated circuit substrate or a doped region of an epitaxial layer on the substrate, or a doped polysilicon layer over the substrate, is covered with an insulating layer. Then contact holes are formed through the insulating layer where the interconnection are desired. A second layer of conducting material is deposited over the insulating layer and the contact holes to make the electrical interconnection. By standard semiconductor processing techniques, the second conducting layer is masked, etched and defined into a conducting line. The second conducting line is typically formed from an aluminum alloy deposited by a sputtering process.
It is in these contact holes that certain types of antifuse structures with near-ideal electrical characteristics may be created. Examples of such antifuse structures are described in a U.S. patent application, filed on Mar. 20, 1991 by the present applicants and assigned to the present assignee, entitled "IMPROVED METHOD OF FABRICATING ANTIFUSES IN AN INTEGRATED CIRCUIT DEVICE AND RESULTING STRUCTURE."
However, as contact hole dimensions have become smaller and smaller, and the desire for greater packing densities has increased, the sidewall angles of the contact holes have become more vertical. Thus the sidewall step coverage of the aluminum layer becomes less and less reliable to the point that a complete discontinuity in the layer becomes possible. This is a major problem limiting yield on sub-micron integrated circuits.
Since the antifuses noted above lie in the contact holes, they must also shrink with contact holes. The antifuse in their current form cannot be manufactured reliably with critical dimensions of smaller than one micron. The present invention makes it possible to manufacture antifuses beyond that limit. The present invention offers highly compact antifuses having integrity in step coverage and highly desirable electrical characteristics.